The present invention relates to a self-recovering current-limiting device with liquids metal, including electrodes made of solid metal for the connection to an external electric circuit to be protected and several compression spaces which are partially filled with liquid metal.
Soviet Union Patent Publication SU 922 911 A describes a self-recovering current-limiting device containing two electrodes made of solid metal which are separated by first insulating bodies which are designed as a pressure-resistant insulating housing. Inside the insulating housing, compression spaces are formed by insulating intermediate walls and second insulating bodies which are arranged therebetween and designed as ring-shaped sealing disks, the compression spaces being partially filled with liquid metal and arranged one behind the other and interconnected via connecting channels of the intermediate walls, the connecting channels being filled with liquid metal and arranged off-center. Thus, in normal operation, a continuous, inner conductive connection exists between the electrodes via the liquid metal. In the current-limiting event, the liquid metal is displaced from the connecting channels as a result of the high current density. In this manner, the electrical connection of the electrodes via the liquid metal is interrupted, resulting in the limiting of the short-circuit current. Subsequent to clearing or eliminating the short circuit, the connecting channels refill with liquid metal whereupon the current-limiting device is operational again. In German Patent Application DE 40 12 385 A1, a current-limiting device having only one compression space is described and vacuum, protective gas, or an insulating liquid are mentioned as the medium above the liquid level. A known current-limiting device according to Soviet Union Patent Publication SU 1 094 088 A is equipped with intermediate walls in which several connecting channels are concentrically formed around, i.e., lie at a same radius from and are symmetrically disposed relative to, the longitudinal axis and with separating walls made of copper which are arranged between the intermediate walls and led outward for cooling the liquid metal. This current-limiting device permits positions of use involving rotations of up to 360 about the horizontal longitudinal axis and inclinations of up to 50 relative to the horizontal, which, however, is rendered possible only in conjunction with the separating walls, which disadvantageously carry a potential, the compression spaces having to be individually filled with liquid metal in a manner requiring too much effort because of these separating walls.
To enable the current-limiting devices mentioned at the outset to be used for different cases of application, they have to be differently designed to the effect that they do not operate in response to an overloading of more or less short duration, depending on the case of application. Thus, for example, in conjunction with generators, current-limiting devices must not operate in response to a short-time overload current which is 2 . . . 6 times the nominal current or, in conjunction with motors of poor iron quality or transformers, in response to a short-time overload current which is 6 . . . 18 times the nominal current, but have to operate only in response to a short-circuit current which in comparison is higher. Until now, therefore, there has been the disadvantageous requirement for the manufacturers to offer a considerable number of current-limiting devices to permit a suitable selection with respect to the conditions on the user side.
According to German Patent Document DE-PS 373 009 a switch in which the contact is made via liquid metal which partially fills the interior and the switching body is provided with a perforated dividing wall which separates the liquid metal. The connecting channels in the dividing wall are uniformly arranged on a reference circle which is concentric with respect to the longitudinal axis of the switch. The two parts of the liquid metal are connected via an adjustable channel cross-section, the adjustment being effected by a rotation about the longitudinal axis of the switch. After a certain quantity of electricity has passed through, the liquid metal in the channel vaporizes and interrupts the current while at the same time a tripping solenoid restores the switch to the non-conducting original position so that the readiness of the switch is attained again only after a new rotation to be effected from outside. This switch has to be reset to the service position using an external device after the current-limiting event has occurred. Secondly, the switch uses a uniformly concentric arrangement of connecting channels. Thirdly, a regulating device, for example, a regulating screw, are required for adjusting a minimum trip current.
The present invention provides a self-recovering current-limiting device with liquid metal. The device includes a first and a second electrode for connection to an electric circuit to be protected, each of the first and second electrodes being made of a respective solid metal. A plurality of pressure-resistant insulating bodies and a plurality of insulating intermediate walls supported by the plurality of insulating bodies are also provided. The plurality of insulating intermediate walls and the plurality of pressure-resistant insulating bodies define a plurality of compression spaces, the plurality of compression spaces being disposed one behind the other between the first and second electrodes and being at least partially filled with the liquid metal. The plurality of insulating intermediate walls define a longitudinal axis extending perpendicularly thereto in a generally horizontal direction and each define a plurality of connecting channels disposed generally non-concentrically relative to the longitudinal axis so as to enable a plurality of positions of use of the current-limiting device to be achieved by turning the current-limiting device about the longitudinal axis, a different current-limiting characteristic being provided in each of the positions of use.
By deliberately installing the current-limiting device in different positions of use, the liquid metal, because of its fluid properties, adapts to the then resulting specific inner spatial geometry of the current-limiting device. It was found that the magnitude of the response, or minimum trip, current increases with increasing filling level of the liquid metal above the connecting channels, provided that the remaining conditions are identical.
Depending on the design and arrangement of the connecting channels, different immersion depths and/or a different number of connecting channels situated below the liquid level ensue.
In an embodiment of the present invention, in one of the positions of use, all connecting channels are situated above the liquid level. By a rotation into this position of use from another position of use or vice versa, the current-limiting devices additionally acts as an on-off switch.
The current-limiting device may be provided with an indicating device assigned to its positions of use and which provides unequivocal information on the current-limiting characteristic of the specific position of use.
GalnSn alloys as the liquid metal to be used are easy to handle because of their physiological harmlessness. An alloy of 660 parts by weight of gallium, 205 parts by weight of indium, and 135 parts by weight of tin is liquid from 10xc2x0 C. to 2000xc2x0 C. at normal pressure and possesses sufficient electrical conductivity.